Why not become a lifetime supporting member of the site with a one-time donation of any amount? Your donation entitles you to a ton of additional benefits, including access to exclusive discounts and downloads, the ability to enter monthly free software drawings, and a single non-expiring license key for all of our programs.

You must sign up here before you can post and access some areas of the site. Registration is totally free and confidential.

I'm not sure if i should be as wowed by this as i am, but while fooling around with screenshots today, i stumbled on a kind of visual illusion.

Look at this normal screenshot of notepad window from windows xp, which has a nice 3d raised effect on the border and on the upper right titlebar buttons, etc.

And now look what happens when you simply rotate it clockwise 180 degrees.. all of a suddent the buttons look like they are indented, etc.. the visual part of brain examining shadows suddenly reinterprets the image, and it looks really strange. at least to me it does -- so much that i had to keep checking to see if i didn't have a bug in my rotation function!

Or maybe i'm the only one who finds this cool and for whom it seems like a visual illusion?

It is surprising how drastic the effect is. When I tilt my head a little and concentrate on a corner of the upside-down version, I can see it properly. But just as I untilt my head, the usual 3d-effect disappears!

After all these years, you're the first to notice that! It really is the "3d raised effect on the border and on the upper right titlebar buttons." Cool. Of course, it doesn't work with simpler schemes, such as Linux-KDE:

@mouser: It is very interesting, and also a coincidence - I was playing around with 180 degree screen rotation the other day, showing my wife the same thing. I also demonstrated using the mouse (which moved "upside down" too). It nearly did my head in.This is a relatively well-known perceptual illusion and is attributable to how the brain interprets what the eyes see. Our eyes actually "see" everything upside-down anyway (the image of what the eye receives is upside-down on the retina at the back of the eye), and the brain learns at an early age to translate the image to the right way up, using light, colour, shadows and lines as reference points and cues to make it all make sense. So what we THINK we see is already a perceptual illusion conjured up by our brain's image-processing system.

What does the trick in the case you show (and you can see it just by turning the screen upside-down) is mainly the shadows around the objects, which give a false sense of 3D right-way-up (it's still all 2D), and the brain adroitly reverses it when it's upside-down, rationally using the same reference points and cues.

You can get a similar illusion by:

Staring at 3D line drawings - they seem to "pop" in and out in your perception.

Staring at that animated image of the silhouette of a slowly spinning woman. Your perception can make her seem to rotate left or right, but not everyone can deliberately change the perceived rotation. She's not rotating in any direction at all, but she looks as though she is.

Some people might say that animated graphics of Angelina Jolie seem to animate more smoothly and look more attractive when she is pictured naked as opposed to clothed, but I couldn't possibly comment.

@lujomu: Yes, a great image. My daughter sometimes videos my chin and mouth upside-down to make it look like a talking face (after drawing some eyes on the bottom of my chin). There are some amusing YouTube clips along the same lines.

Fascinating! I remember having fun with a similar kind of illusion from when I was a kid. I think it has something to do with how we're used to thinking of light hitting objects from the upper-left hand side. In my recent explorations into drawing and shading, I've learned that the default way to shade is to assume the light is coming from the upper left.

In my recent explorations into drawing and shading, I've learned that the default way to shade is to assume the light is coming from the upper left.

Well, in Nature, the light source moves from East to West, and is higher than us, or "overhead" most of the time, so that assumption is probably at least two-thirds true! Except perhaps at sunrise or sunset when the light is almost on the horizontal, or in far north and far south parts of the world when they get those long winters with the sun seemingly barely able to lift itself off the horizon. Oh, and in Hammer horror films where the light often seems to mysteriously come from below/underneath when anything scary is going on...

I seem to recall that the neurophysiology course dealt with the automatic interpretation that shadowing comes from an overhead light source. There are oodles of these essential processes about which we are unaware.

This specific illusion is employed in nature as camouflage and mimicry.